Research Article Improvement in the Mechanical Properties of High Temperature Shape Memory Alloy (Ti 50 Ni 25 Pd 25 ) by Copper Addition

Transcription

1 Advances in Materials Science and Engineering Volume 215, Article ID , 7 pages Research Article Improvement in the Mechanical Properties of High Temperature Shape Memory Alloy (Ti 5 Ni 25 Pd 25 ) by Copper Addition Saif ur Rehman, 1 Mushtaq Khan, 1 A. Nusair Khan, 2 Syed Husain Imran Jaffery, 1 Liaqat Ali, 1 and Aamir Mubashar 1 1 School of Mechanical and Manufacturing Engineering (SMME), National University of Science and Technology (NUST), Islamabad44,Pakistan 2 Institute of Industrial Control System, Rawalpindi 46, Pakistan Correspondence should be addressed to Mushtaq Khan; mkhan nust@yahoo.com Received 28 November 214; Accepted 2 February 215 Academic Editor: Rui Vilar Copyright 215 Saif ur Rehman et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. High temperature shape memory alloys Ti 5 Ni 25 Pd 25 and Ti 5 Ni 2 Pd 25 Cu 5 were developed, characterized, and tensile tested in both martensite (M f 5 C) and austenite (A f +5 C) phases. The transformation temperatures of ternary Ti 5 Ni 25 Pd 25 alloy were increased by 11 to 12.5 C by substitution of Ni with 5 at% Cu. At the same time, transformation heat absorbed and released during forward and reverse martensitic transformation was also increased. In the martensite phase, the mechanical properties, that is, the stress for reorientation of martensite variants and fracture stress, were increased by 33 and 6 MPa, respectively, whereas the fracture strain was decreased by 1.5%. In the austenite phase, the critical stress for slip and fracture stress were increased by 62 and 4.9 MPa, respectively, whereas the fracture strain was decreased by 1.2%. The increase in both stresses was attributed to the solid solution strengthening by substitution of Ni atoms with relatively greater atomic radius of copper (Cu) atoms. The overall results suggest that the addition of 5 at% Cu in place of Ni in Ti 5 Ni 25 Pd 25 alloy is very beneficial to improving the mechanical and shape memory properties and increasing the transformation temperatures. 1. Introduction NiTi shape memory alloys are widely used in many engineering and medical fields due to their outstanding superelastic and shape memory properties [1]. Recently, the application of NiTi alloys has been extended in the industries like power generation, automotive, oil and gas exploration, and aerospace as solid state actuators [2 4]. However, in the mentioned applications, the actuators are to be operated at higher temperature due to high temperature environment (temperature greater than 1 C). Therefore, it is needed for the NiTi shape memory alloys to raise their phase transformation temperatures. The transformation temperatures ofthenitibasealloyshavebeensuccessfullyincreasedby alloying with some elements like Pd, Pt, Au, Zr, and Hf [5 1]. However, alloying of Pd and Pt has got relatively more attention as compared to other ternary alloying elements, due to its comparable properties of high work output and good workabilitylike NiTi alloys [11 14]. In addition to these properties, TiNiPd has narrow thermal hysteresis which is desired for fast and active control of actuators [11]. As the actuators are exposed to high temperature environment during operation, therefore, for reliable and long-life performance, it is necessary for the high temperature SMAs to have microstructural stability and resistance to oxidation at elevated temperatures. It should have enough strength in the martensite phase to resist transformation induced plasticity [15]. Apart from that, it should also have high critical stress for slip deformation to resist recovery, recrystallization, and creep in the high temperature austenite phase. The proposed techniques for strengthening the alloy against plastic deformation, thermal driven mechanisms and enhancing the

2 2 Advances in Materials Science and Engineering dimensional stability include solid solution strengthening [16 19], precipitation hardening [2, 21], thermomechanical treatment [21], and annealing after cold working [22]. Alloying of different quaternary elements to TiNiPd has been thoroughly investigated by very few researchers [11, 16 19]. Solid solution strengthening has been carried out by addition of.12 and.2 at% boron in TiNiPd [16, 17]. It has been reported that the ductility of TiNiPd alloy at room and high temperature was improved due to formation of fine TiB 2 precipitates. Due to addition of boron, grain size of the alloywasrefinedandresultedinimprovedultimatetensile strength; however, no improvement in the shape memory properties was observed. Substitution of.5 at% scandium with Ti in Ti 5.5 Ni 24.5 Pd 25 high temperature shape memory alloys has been reported by Atli et al. [11]. By addition of scandium, the transformation temperatures were decreased by 6 CinM s and 1 CinM f. The strength against irreversible deformation was observed to be improved as compared with ternary base alloy. Both the ternary Ti 5.5 Ni 24.5 Pd 25 and quaternary Ti 5 Ni 24.5 Pd 25 Sc.5 alloys exhibited very narrow thermal hysteresis as compared to NiTi binary alloys. The effects of addition of 1. at% scandium in place of Ti in Ti 5.3 Ni 24.7 Pd 25 on microstructure and transformation temperatures were also investigated by Ramaiah et al. [23]. It was reported that the transformation temperatures were significantly decreased by 42 C; M f temperature of 181 C of ternary Ti 5.3 Ni 24.7 Pd 25 base alloy decreased to 139 Cfor quaternary Ti 49.3 Ni 24.7 Pd 25 Sc 1. alloy. However, at the same time, thermal hysteresis also decreased from 15 Cto7 C. The effects of 5 and 1 at% copper addition in Ti 5 Ni 25 Pd 25 onthemicrostructureandshapememorypropertieswere studied. It has been reported that strength of B19 martensite and transformation temperature are slightly increased but thethermalhysteresisremainedthesame.itwasalsonoted that addition of Cu increases the dimensional stability of alloy at higher stress levels due to increasing the resistance against viscoplastic deformation by solid solution hardening mechanism [18]. In our previous work [21, 24], it has been shown that after thermomechanical training and precipitation hardening process thermal stability and recovery ratio were improved significantly in Ti 5 Ni 15 Pd 25 Cu 1 alloys; however, the transformation temperatures were decreased. To improve the shape memory properties of alloys, it is important to add such a solid solution strengthening agent thatincreasestheyieldstressinaustenitephase(critical stress for slip) and decreases the yield stress (stress for reorientation of martensite variant) in martensite phase. By this way, if the difference between the critical stress for slip and stress required for reorientation is increased, the shape memory properties will be improved. However, for this purpose it is necessary to investigate the mechanical properties (critical stress for slip and stress required for reorientation of martensite variants) in austenite phase (above A f temperature) and martensite phase (below M f temperature), respectively. In the present study, the effect of substitution of Ni with 5 at% Cu in Ti 5 Ni 25 Pd 25 was investigated for low and high temperature mechanical properties and phase transformation temperatures. 2. Materials and Methods Ti 5 Ni 25 Pd 25 and Ti 5 Ni 2 Pd 25 Cu 5 high temperature shape memory alloys were prepared by vacuum arc melting process using tungsten electrode and water cooled copper crucible. High purity elemental constituents wt.% Ti, wt.% Ni,99.99wt.%Pd,and99.99wt.%Cuwereusedforpreparation of these alloys. The cast buttons were melted 6 times and turned over after each melting cycle to ensure alloying homogeneity. The cast buttons were sealed in quartz tube after being vacuumed, filled with argon gas, and then homogenized at 95 C for 2 hours and water quenched. The homogenized buttons were sliced into.4 mm thick strips by wire electrical discharge machine (EDM). The.4 mm thick strips were cold rolled by 25% and their thickness was reduced to.3 mm. Samples for differential scanning calorimetry (DSC) and tensile testing were machined using wire EDM. All the samples were solution treated at 9 Cfor1 hour and quenched in cold water without breaking the quartz tubes. Phase transformation temperatures of both alloys in the solution treated condition were determined by DSC at a heating/cooling rate of 5 C/min under vacuum. The sample size for DSC analysis was kept as 2 mm 2mm.3 mm. Isothermal tensile tests were performed to measure the mechanical behavior using tensile and compression testing machineequippedwithmtscontrollerandsoftware.inhouse designed and manufactured holding grips were used togripthesamples.loadcellof1knwasusedandstrain measurement in tension was carried out by the movement of crosshead directly. Samples were heated by induction process and a K-type thermocouple was attached directly to the central portion of the samples by wrapping the copper wire for temperature measurement. Aftergrippingthesampleandattachingthermocouple, each sample was heated at required isothermal test temperaturewhilecontrollingloadatn.thesampleswereallowed to stay at isothermal test temperature for 5 minutes to stabilize the thermal fluctuations. The samples were strained at a strain rate of mm/sec. For both alloys, only two isothermal tensile tests were performed, one at 5 CbelowM f and one at 5 CaboveA f. 3. Results and Discussion 3.1. Effect of Cu Addition on Transformation Temperatures. DSC analysis was carried out to investigate the effect of 5 at% Cu addition on phase transformation temperatures of Ti 5 Ni 25 Pd 25. Figure 1 shows the DSC heating and cooling cycles for Ti 5 Ni 25 Pd 25 and Ti 5 Ni 2 Pd 25 Cu 5,withsolution treated at 9 C for 1 h. Phase transformation temperatures (M s,martensitestart;m f,martensitefinish;a s, austenite start; and A f, austenite finish) of both of the samples were measured from the intersection of the base line and the linear portions of exothermic or endothermic peaks as shown in Figure 1. The measured transformation temperatures of Figure 1 were summarized in Table 1 to compare the change in transformation temperatures for Ti 5 Ni 2 Pd 25 Cu 5 with respect to the baseline Ti 5 Ni 25 Pd 25 alloy. Both alloys

3 Advances in Materials Science and Engineering 3 Heat flow (mw/mg) exo up.2 Ti 5 Ni 2 Pd 25 Cu 5 Ti 5 Ni 25 Pd 25 M f A s M s A f Heating Cooling Table 1: Transformation temperatures determined from DSC cooling and heating cycles of Figure 1 for Ti 5 Ni 25 Pd 25 and Ti 5 Ni 2 Pd 25 Cu 5. Alloy Transformation temperatures ( C) Thermal hysteresis M s M f A s A f A f M s Ti 5 Ni 25 Pd Ti 5 Ni 2 Pd 25 Cu Temperature ( C) Figure 1: DSC heating and cooling curves showing the transformation temperatures of Ti 5 Ni 25 Pd 25 and Ti 5 Ni 2 Pd 25 Cu 5 alloys. exhibited very similar behavior with single-stage martensite transformation and demonstrated proper developed peaks with well calculated transformation temperatures. However, the transformation heat (ΔH c ) released (area under cooling curve) during forward transformation cycle and transformation heat (ΔH h ) absorbed (area under heating curve) during reverse transformation cycle for Ti 5 Ni 2 Pd 25 Cu 5 are greater than those of Ti 5 Ni 25 Pd 25. The transformation temperatures of quaternary Ti 5 Ni 2 Pd 25 Cu 5 alloy are 11 to 12.5 Candare higher than the ternary baseline Ti 5 Ni 25 Pd 25 alloy as shown in Table 1.TheM s temperature of Ti 5 Ni 25 Pd 25 increased by 12.5 Cfrom142.5 Cto155 C, while the A f temperature increased by 11 Cfrom167 Cto178 C upon addition of 5 at% Cu in place of Ni. From the above experimental results, it has been observed that substitution of Ni by 5 at% Cu increased the transformation temperatures and transformation heats significantly. The changes in transformation temperatures and transformation heats are actually due to the change in Ni/Pd content, because Cu content does not affect the transformation temperatures [25]. In the referred study, it has been reported that, according to the TiNi-TiPd pseudobinary phase diagram, the increase in Pd content and decrease in Ni content increase the transformation temperatures [26]. Moreover, according to Clausius-Clapeyron equation, the increase in transformation temperature causes increases in the transformation heats [26]. Thus, the increase in Ni/Pd ratio (as Ni content decreased and Pd content remained constant) resulted in increase in transformation temperatures and transformation heats absorbed and released during forward and reverse martensitic transformation, respectively. Moreover, it can also be noted from Table 1 that, by substitution of Ni with 5 at% Cu, the thermal hysteresis decreased by 1.5 Cfrom 24.5 Cto23 C. 3.2.EffectofCuAdditiononMechanicalProperties.It is important to investigate the mechanical properties of shape memory alloys in both phases, that is, martensite and austenite, because the stress-strain relations in both phases are different from each other. Other conventional structural materials like steel have maximum yield strength at room temperature and then it decreases by increasing the testing temperature above 1 C. Conversely, for high temperature shape memory alloys, the yield strength at room temperature in martensite phase (lower than M f )mustbelessthan the yield strength at higher temperature (greater than A f ) in austenite phase. Austenite yield strength represents the critical stress for slip deformation while martensite yield strength represents critical stress for shear of martensite twins. For feasible actuators, the critical stress for shear must be lower than the critical stress for slip, so that when stress is applied, it results in shape deformation by shear of martensite twins rather than via dislocation generation and movement. Tensile stress-strain curves tested in the martensite condition, 5 CbelowM f for Ti 5 Ni 25 Pd 25 and Ti 5 Ni 2 Pd 25 Cu 5 alloys, are shown in Figure 2. The yield stress for both alloys was calculated by drawing a parallel line,.2% offset to the elastic region of stress-strain curve as shown in Figure 2.The.2% yield stress (σ y ) calculated from these curves in the martensitic condition for both alloys is shown in Table 2.This yield stress corresponds to the stress required for reorientation of martensite twins (also called stress for detwinned martensite). From Table 2,itcanbeobservedthatmartensite yield stress of Ti 5 Ni 2 Pd 25 Cu 5 was increased by 33 MPa withrespecttothebaselineti 5 Ni 25 Pd 25 alloy. Similarly, the stress at which the fracture occurred in the material (σ f ) also increased by 6 MPa; MPa for Ti 5 Ni 25 Pd 25 was increased to MPa for Ti 5 Ni 2 Pd 25 Cu 5.However,the strain at which the fracture occurred in the material (ε f )was decreased by.75%; fracture strain of 1% for Ti 5 Ni 25 Pd 25 was decreased to 9.25% for Ti 5 Ni 2 Pd 25 Cu 5. Figure 3 represents the tensile stress-strain curves tested in the austenite condition, 5 CaboveA f for Ti 5 Ni 25 Pd 25 and Ti 5 Ni 2 Pd 25 Cu 5 alloys. Measurement of austenite yield strength was carried out by the same procedure as discussed earlier and as shown in Figure 3. The.2%yield stress (σ y ) calculated from these curves in the austenitic condition for both alloys is shown in Table 2. Thisyield stress represents the critical stress for slip; stress required for the deformation of material through dislocations generation and their movement. The austenite yield stress of 44 MPa for Ti 5 Ni 25 Pd 25 was increased to 52 MPa for Ti 5 Ni 2 Pd 25 Cu 5 and this resulted in net increase of 62 MPa as shown in Table 2.Thefracturestress(σ f )alsoincreased by 4.9 MPa; MPa for Ti 5 Ni 25 Pd 25 was increased to MPa for Ti 5 Ni 2 Pd 25 Cu 5.Here,thefracturestrain(ε f ) wasobservedtobedecreasedby1.2%;fracturestrainof8.5% for Ti 5 Ni 25 Pd 25 was decreased to 7.3% for Ti 5 Ni 2 Pd 25 Cu 5.

4 4 Advances in Materials Science and Engineering 12 Ti 5 Ni 25 Pd Ti 5 Ni 2 Pd 25 Cu M f = 119 C Testing temperature =69 C M f =133 C Testing temperature =83 C (a) (b) Figure 2: Tensile stress-strain curves tested in the martensite condition, 5 CbelowM f of (a) Ti 5 Ni 25 Pd 25 and (b) Ti 5 Ni 2 Pd 25 Cu 5 alloys. Table 2: Yield stress, fracture stress, and fracture strain calculated from stress-strain curves of Figures 2 and 3 for Ti 5 Ni 25 Pd 25 and Ti 5 Ni 2 Pd 25 Cu 5 alloys. Alloy Phase Testing temperature ( C).2% Yield stress, σ y (MPa) Fracture stress, σ f (MPa) Fracture strain, ε f (%) Ti 5 Ni 25 Pd 25 Martensite Austenite Ti 5 Ni 2 Pd 25 Cu 5 Martensite Austenite From the experimental results shown above, it can be observed that, by substitution of 5 at% Ni by 5 at% Cu, the yield stress and fracture stress in the martensite phase were increased by 33 and 6 MPa, respectively, whereas the fracture strain was decreased by 1.5%. Similarly the yield stress and fracture stress in the austenite phase were increased by 62 and 4.9 MPa, respectively, whereas the fracture strain was decreased by 1.2%. The increase in both yield stresses (stress for reorientation of martensite and stress for slip deformation) and fracture stress (maximum stress) is attributed to the solid solution strengthening due to partial substitution of Ni with Cu. Here, the atomic radius of Cu (.128 nm) is relatively greater than the atomic radius of Ni (.125 nm) and is therefore responsible for solid solution strengthening. By solution strengthening effect, the ductility of Ti 5 Ni 2 Pd 25 Cu 5 was lowered and resulted in relatively low fracture strain in both phases. Itcanbeobservedthattheincreaseinstressforreorientation of martensite variants (although it is not required for better shape memory alloys) was observed to be 33 MPa. On the other hand, the critical stress for slip deformation (essentially required for better shape memory alloys) was increased by 62 MPa (Table 2).Astheincreaseincritical stress for slip is more beneficial than the increase in stress for reorientation of martensite variants, it can be suggested that, by partial substitution of 5 at% Ni with 5 at% Cu, the critical stress for slip was increased by 29 MPa (difference in net increase in critical stress for slip and net increase in the stress for reorientation of martensite variants). Figure 4 represents the tensile stress-strain curves (loading and unloading for 5 complete cycles) tested in the austenite condition, 5 C above A f of Ti 5 Ni 25 Pd 25 and Ti 5 Ni 2 Pd 25 Cu 5 alloys. For both alloys, the samples were first stressed continuously until the strain reached at 5% and were then unloaded completely. This process was repeated fivetimesforbothalloys.itcanbeobservedthatboth alloys resulted in partial pseudoelasticity. The maximum stress 676 MPa reached at 5% strain for Ti 5 Ni 25 Pd 25 in the first loading cycle is lower than the stress 82 MPa reached at 5% strain for Ti 5 Ni 2 Pd 25 Cu 5.Moreover,the stress hystereses that resulted in the first, third, and fifth cycles for Ti 5 Ni 25 Pd 25 alloy are 236, 21, and 19 MPa, respectively. Similarly, the stress hystereses obtained in the first, third, and fifth cycles for Ti 5 Ni 2 Pd 25 Cu 5 alloy are 182, 16, and 16 MPa, respectively. Comparing the stress hysteresis of both alloys, it can be observed that the stress hystereses for Ti 5 Ni 25 Pd 25 were larger and continuously decreased as the number of cycles increased, whereas the stress hystereses for Ti 5 Ni 2 Pd 25 Cu 5 were smaller and remained stable. Thus, it canbeconcludedthat,bysubstitutionofniby5at%cu in Ti 5 Ni 25 Pd 25 alloy, the stress hysteresis was reduced and became stable.

5 Advances in Materials Science and Engineering Ti 5 Ni 25 Pd 25 Ti 5 Ni 2 Pd 25 Cu A f =167 C Testing temperature = 217 C A f =178 C Testing temperature = 228 C (a) (b) Figure 3: Tensile stress-strain curves tested in the austenite condition, 5 CaboveA f of (a) Ti 5 Ni 25 Pd 25 and (b) Ti 5 Ni 2 Pd 25 Cu 5 alloys. 1 Ti 5 Ni 25 Pd 25 1 Ti 5 Ni 2 Pd 25 Cu 5 N=1 N=3 N=5 5 N=1 N=3 N= (a) (b) Figure 4: Tensile stress-strain curves (loading and unloading) tested in the austenite condition, 5 CaboveA f of (a) Ti 5 Ni 25 Pd 25 and (b) Ti 5 Ni 2 Pd 25 Cu 5 alloys. N representsnumberofcycles. 4. Conclusions High temperature shape memory alloys Ti 5 Ni 25 Pd 25 and Ti 5 Ni 2 Pd 25 Cu 5 weredevelopedandcharacterizedformeasurement of phase transformation temperatures. They were tensile tested to investigate their mechanical properties in both martensite (M f 5 C) and austenite (A f +5 C) phases. The important conclusions drawn are reported as follows. (1) The transformation temperatures of ternary Ti 5 Ni 25 Pd 25 alloy were increased by 11 to 12.5 C by substitution of Ni with 5 at% Cu; M s temperature of Ti 5 Ni 25 Pd 25 increased by 12.5 Cfrom142.5 Cto 155 C, while the A f temperature increased by 11 C from 167 Cto178 C. The increase in transformation temperatures was attributed to the decrease of Ni content and increase of Ni/Pd content in the matrix. (2) The transformation heat absorbed and released during forward and reverse martensitic transformation was increased by substitution of Ni with 5 at% Cu. (3) In the martensite phase, the stress for reorientation of martensite variants and fracture stress were increased by 33 and 6 MPa, respectively, whereas the fracture strain was decreased by.75%. In the austenite phase,

6 6 Advances in Materials Science and Engineering the critical stress for slip and fracture stress were increased by 62 and 4.9 MPa, respectively, whereas thefracturestrainwasdecreasedby1.2%,showingthe improvement in mechanical properties. (4)Theincreaseinbothstresseswasattributedtothe solid solution strengthening by substitution of Ni atoms with relatively greater atomic radius of Cu atoms. (5) The relatively larger increase in the critical stress for slip by substitution of Ni with 5 at% Cu suggested that the shape memory properties were improved. (6)BysubstitutionofNiby5at%CuinTi 5 Ni 25 Pd 25 alloy, the stress hysteresis was reduced and became stable. The overall results suggested that addition of 5 at% Cu in place of Ni in Ti 5 Ni 25 Pd 25 alloy is very beneficial to improving themechanicalandshapememorypropertiesofthealloy.it also increased the transformation temperatures of alloy to a reasonable level. Conflict of Interests The authors declare that there is no conflict of interests regarding the publication of this paper. References [1]S.Miyazaki,K.N.Melton,D.Stockel,andC.M.Waymann, Butterworth-Heinemann,London, UK, 199. [2] J. Ma, I. Karaman, and R. D. Noebe, High temperature shape memory alloys, International Materials Reviews, vol.55,no.5, pp , 21. [3]T.S.QuackenbushandR.McKillipJr., Selectedapplications of aeropropulsion actuation and shape control devices using HTSMAs, Metallurgical and Materials Transactions A, vol. 43, no. 8, pp , 212. [4] L. Kovarik, F. Yang, A. Garg et al., Structural analysis of a new precipitate phase in high-temperature TiNiPt shape memory alloys, Acta Materialia, vol. 58, no. 14, pp , 21. [5]D.Golberg,Y.Xu,Y.Murakami,K.Otsuka,T.Ueki,and H. Horikawa, High-temperature shape memory effect in Ti 5 Pd 5-x Ni x (x = 1, 15, 2) alloys, Materials Letters, vol.22, no. 5-6, pp , [6] Y. Xu, S. Shimizu, Y. Suzuki, K. Otsuka, T. Ueki, and K. Mitose, Recovery and recrystallization processes in Ti-Pd-Ni hightemperature shape memory alloys, Acta Materialia,vol.45,no. 4, pp , [7] J.A.DeCastro,K.J.Melcher,R.D.Noebe,andD.J.Gaydosh, Development of a numerical model for high-temperature shape memory alloys, Smart Materials and Structures, vol. 16, no. 6, pp , 27. [8] A. Stebner, S. Padula II, R. Noebe, B. Lerch, and D. Quinn, Development, characterization, and design considerations of Ni 19.5 Ti 5.5 Pd 25 Pt 5 high-temperature shape memory alloy helical actuators, Intelligent Material Systems and Structures,vol.2,no.17,pp ,29. [9] K.C.Atli,I.Karaman,R.D.Noebe,A.Garg,Y.I.Chumlyakov, and I. V. Kireeva, Shape memory characteristics of Ti 49.5 Ni 25 Pd 25 Sc.5 high-temperature shape memory alloy after severe plastic deformation, Acta Materialia, vol. 59, no. 12, pp , 211. [1] B. Kockar, K. C. Atli, J. Ma et al., Role of severe plastic deformation on the cyclic reversibility of a Ti 5.3Ni33.7Pd16 high temperature shape memory alloy, Acta Materialia, vol. 58, no.19,pp ,21. [11] K. C. Atli, I. Karaman, R. D. Noebe, A. Garg, Y. I. Chumlyakov, and I. V. Kireeva, Improvement in the shape memory response of Ti 5.5 Ni 24.5 Pd 25 high-temperature shape memory alloy with scandium microalloying, Metallurgical and Materials Transactions A, vol. 41, no. 1, pp , 21. [12] G. S. Bigelow, S. A. Padula II, A. Garg, D. Gaydosh, and R. D. Noebe, Characterization of ternary NiTiPd high-temperature shape-memory alloys under load-biased thermal cycling, Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science,vol.41,no.12,pp ,21. [13] K. C. Atli, B. E. Franco, I. Karaman, D. Gaydosh, and R. D. Noebe, Influence of crystallographic compatibility on residual strain of TiNi based shape memory alloys during thermomechanical cycling, Materials Science and Engineering A, vol. 574, pp. 9 16, 213. [14] K. C. Atli, I. Karaman, and R. D. Noebe, Work output of the two-way shape memory effect in Ti 5.5 Ni 24.5 Pd 25 hightemperature shape memory alloy, Scripta Materialia, vol. 65, no.1,pp.93 96,211. [15] K. Otsuka, K. Oda, Y. Ueno, M. Piao, T. Ueki, and H. Horikawa, The shape memory effect in a Ti 5 Pd 5 alloy, Scripta Metallurgica et Materiala,vol.29,no.1,pp ,1993. [16] W.S.YangandD.E.Mikkola, DuctilizationofTi-Ni-Pdshape memory alloys with boron additions, Scripta Metallurgica et Materialia,vol.28,no.2,pp ,1993. [17] Y.Suzuki,Y.Xu,S.Morito,K.Otsuka,andK.Mitose, Effects of boron addition on microstructure and mechanical properties of Ti-Td-Ni high-temperature shape memory alloys, Materials Letters, vol. 36, no. 1-4, pp , [18] I.M.Khan,H.Y.Kim,T.-H.Nam,andS.Miyazaki, EffectofCu addition on the high temperature shape memory properties of Ti 5 Ni 25 Pd 25 alloy, Alloys and Compounds, vol.577, supplement 1, pp. S383 S387, 213. [19] K. V. Ramaiah, C. N. Saikrishna, and S. K. Bhaumik, Microstructure and transformation behaviour of Ni 75 X Ti X Pd 25 high temperature shape memory alloys, Alloys and Compounds,vol.554,pp ,213. [2] S. Shimizu, Y. Xu, E. Okunishi, S. Tanaka, K. Otsuka, and K. Mitose, Improvement of shape memory characteristics by precipitation-hardening of Ti-Pd-Ni alloys, Materials Letters, vol. 34, no. 1-2, pp , [21] M. Imran Khan, H. Y. Kim, T. H. Nam, and S. Miyazaki, Formation of nanoscaled precipitates and their effects on the high-temperature shape-memory characteristics of a Ti 5 Ni 15 Pd 25 Cu 1 alloy, Acta Materialia, vol.6,no.16,pp , 212. [22] M. I. Khan, H. Y. Kim, Y. Namigata, T.-H. Nam, and S. Miyazaki, Combined effects of work hardening and precipitation strengthening on the cyclic stability of Ti Ni Pd Cu-based high-temperature shape memory alloys, Acta Materialia, vol. 61, no. 13, pp , 213. [23] K. V. Ramaiah, C. N. Saikrishna, J. Bhagyaraj, and S. K. Bhaumik, Influence of Sc addition on microstructure and transformation behaviour of Ni 24.7 Ti 5.3 Pd 25. high temperature shape memory alloy, Intermetallics, vol. 4, pp. 1 18, 213.

7 Advances in Materials Science and Engineering 7 [24] S. U. Rehman, M. Khan, A. N. Khan et al., Transformation behavior and shape memory properties of Ti 5 Ni 15 Pd 25 Cu 1 high temperature shape memory alloy at various aging temperatures, Materials Science and Engineering A, vol. 619, pp , 214. [25] O. Mercier and K. N. Melton, The substitution of Cu for Ni in NiTi shape memory alloys, Metallurgical Transactions A, vol. 1, no. 3, pp , [26] K. Otsuka and C. M. Wayman, Shape Memory Materials, Cambridge University Press, Cambridge, Mass, USA, 1998.

8 Nanotechnology International International Corrosion Polymer Science Smart Materials Research Composites Metallurgy BioMed Research International Nanomaterials Submit your manuscripts at Materials Nanoparticles Nanomaterials Advances in Materials Science and Engineering Nanoscience Scientifica Coatings Crystallography The Scientific World Journal Textiles Ceramics International Biomaterials